Vulcanization accelerator



Patented May 27, 1941 VULCANIZATIO'N ACCELERATOR Robert L. Sibley, Nitro, W. Va., assignor to Monsanto Chemical Company, St. Louis, M0., a

corporation of Delaware No Drawing.

Application December 23, 1937,

Serial No. 181,368

Claims.

The present invention relates to a new and improved class of rubber vulcanization accelerators, to a process of vulcanizing rubber or a rubber containing material, and to the vulcanized rubber products obtained with the aid of said new and improved vulcanization accelerators.

The accelerators of the present invention are the products obtainable by reacting a cyclohexylamine with can aldehyde and further reacting the product so obtained with carbon bisulfide. The use of products obtained by reacting certain amines with an aldehyde and further reacting the product so formed with carbon bisulfide is well-known to the rubber vulcanization art and some of the accelerators employed by the trade are of this type. The use of the accelerators of the present invention, however, represents an improvement over the prior art. As illustrative of this improvement the product obtained by reacting N-methyl cyclohexylamine first with formaldehyde and then reacting the aldehyde-amine with carbon bisulfide has been found on testing to give a faster cure at a lower temperature than the amine-aldehyde, carbon bisulfide reaction products heretofore employed, as for example piperidine reacted with formaldehyde and further reacted with carbon bisulfide. Further advantages of the preferred class of accelerators will be apparent from the examples hereinafter shown.

Typical examples of cyclohexylamines which may be employed in the preparation of the new and preferred class of accelerators are cyclohexylamine, N-methyl cyolohexylamine, N -ethyl cyclohexylamine N-butyl cyolohexylamine, N-amyl cyclohexylamine, dicyclohexylamine, N-benzyl cyclohexylamine, N-hexahydro benzyl cyclohexyl amine, N-methyl, methyl cyclohexylamine and N-ethyl, ethyl cyclohexylamine.

A cyclohexylamine as illustrated above may be reacted with an aldehyde, preferably formaldehyde, and then with carbon bisulfide to form the new and preferred class of accelerators. Examples of aldehydes which may be so employed are formaldehyde, acetaldehyde, and their polymeric forms, propionaldehyde, butylaldehyde, iso valeric aldehyde, acrolein aldehyde, croton aldehyde, aldol, benzaldehyde, cinnamic aldehyde and furfuraldehyde.

As a specific embodiment which is intended to be illustrative of the invention and not limitative of the scope thereof, one of the preferred class of accelerators was prepared from N-ethyl cyclohexylamine. 64 parts by weight of N -ethyl cyclohexylamine (substantially 0.5 molecular proportion) and 28 parts by weight of approximately 37% formaldehyde (substantially 0.28 molecular proportion) were mixed together in a suitable container, keeping the temperature of the mixture below 15 0., and stirred for one hour. The mixture was then allowed to stand overnight at room' temperature at which time it had separated into two layers. The water layer was removed and the oil residue dried over anhydrous sodium sulfate. 19 parts by weight (substantially 0.25 molecular proportion) of carbon bisulfide were then added to the above described oil. The reaction took place immediately and the desired reaction product was obtained :as a clear yellow oil.

As a further specific example of the invention N-methyl cyclohexylamine was reacted in a man.- ner analogous to that described above. 57 parts by weight (substantially 0.5 molecular proportion) of N -methyl cyclohexylamine and 28 parts by weight of approximately 37% formaldehyde (substantially 0.28 molecular proportion) were mixed together in a suitable container. The temperature of the mixture was kept below 15 C. and the mixture was stirred for one hour and allowed to stand until it had separated into two layers.

Stock Rubber as 60% latex lOO Zinc oxlde l Sulfur 1. 5 1. 5 Reaction product of N -ethyl cyclohexylamine and formaldehyde, further reacted with carbon bisulfide. 0. 47 Reactmn product of N methyl cyclohexylamine and formaldehyde, further reacted with carbon bisulfide. 0'. 45

The rubber mixes so compounded were poured on glass to form films and the films dried in air three days at room temperature after which the dry films were cured in air at C. and also in I water at 100 C. The following modulus and tensile properties were found on testing the cured rubber products.

Table I Cured in air at 158 F. (70 0.).

Modulus of elasticity Cure in lbsJin. at elongations of- Tensile at Ult.

breal; in elong., T lbs/in. percent me in Stock minutes 500% 700% A Uncured 640 2470 6130 930 B Uncured 720 2900 6280 910 A 10 630 2450 6190 935 B 10 690 2820 6200 905 A 20 640 2430 6160 935 B 20 700 2860 6050 900 A 30 600 2450 6060 030 B 30 730 2810 6220 905 A 50 630 2440 6020 930 B 50 740 2830 6230 910 A 70 620 2460 6190 935 B 70 760 2970 6470 900 A 90 600 2450 6190 940 B 90 770 3000 6550 910 Table II Cured in water at 100 C.

Modulus of elasticity Cure in 1bs./in. at elongations oi- Tensile at Ult.

break in along, T lbs/in. percent ime 1D Stock minutes 500% 700% A Uncured 600 2200 6030 940 B Uncured 690 2700 6360 900 A 610 2220 6280 945 B 3 710 2720 6430 900 A 5 600 2110 5920 925 B 5 720 2740 6180 885 A 610 2120 6070 930 B 10 710 2740 6400 885 A 590 2210 6080 920 B 15 720 2770 5950 850 A 600 2220 '6070 915 B 20 740 2790 5960 855. A 40 610 2290 5750 880 B 40 810 2930 5800 845 The above data show the accelerating proper ties of the preferred class of materials, for example the reaction product of N-methyl cyclohexylamine and formaldehyde further reacted with carbon bisulfide, when employed in an aqueous rubber dispersion. The data show that the new accelerators are very fast, fiat-curing accelerators. Thus the three day drying at room temperature has resulted in a set-up of the rubber stock and said drying alone produced a high modulus and tensile stock from which it is evident that the new class of accelerators are active at temperatures even below 70 C. The modulus and tensile properties remain nearly constant after curin in air at 70 C. and in Water at 100 C. as shown.

As further specific embodiments of the invention, other typical examples of the preferred class of materials were prepared wherein the amine was initially reacted with the aldehyde and the product so formed further reacted with carbon bisulfide. Thus, by the method hereinbefore described N-ethyl cyclohexylamine was reacted with butylaldehyde and carbon bisulfide and N-benzyl cyclohexylamine was reacted with formaldehyde and carbon bisulfide. The proportions of the reactants employed were substantially two molecular proportions of amine, one molecular proportion of aldehyde and an excess over one molecular proportion of carbon disulfide, the excess being removed from the final product.

Stock Smoked sheets Zinc oxide Sulfur Stearic acid Reaction product of N-rnethyl cyclohexylamine and formaldehyde further reacted with carbon bisulfide Reaction product of N-ethyl cyclohexylamine and butylaldehyde further reacted with carbon bisulfide Reaction product of N-benzyl cyclohexylamine and formaldehyde further reacted with carbon bisulfide The stocks so compounded were vulcanized at the temperature of 5 pounds steam pressure per square inch and the following modulus and tensile properties obtained on testing the cured rubber product.

Table III Modulus of elasticity in Cure lbs/in} at elongations Tensile at Ult.

break in elong., T lbs/in. percent ime 1D Stock minutes 300% 500% O 10 140 250 2725 900 D 10 165 1800 940 E 10 230 2325 020 G 20 185 415 3850 840 D 20 316 2700 880 E 20 150 300 3525 885 C 30 225 590 4500 805 D 30 375 3150 830 E 30 420 3950 850 C 60 360 1300 4550 690 D 00 290 850 3825 720 E 60 260 720 4400 780 The above data show that the preferred class of accelerators give a fast cure at the temperature of five pounds of steam pressure per square inch.

As further specific embodiments of the invention dicyclohexylamine was reacted with formaldehyde and the product so formed reacted with carbon bisulfide; cyclohexylamine was reacted with formaldehyde and the product so formed reacted with carbon bisulfide; 'cyclohexylamine was reacted with acetaldehyde and the product so formed reacted with carbon bisulfide and the materials so prepared found on testing in a typical rubberstock to exhibit desirable accelerating proper-ties.

Ihe presentinvention is not limited to the specific examples hereinbefore set forth wherein the preferred accelerators are employed. Other proportions of the reactants may be employed in the preparation of'the preferred class of accelerators, for example an excess of either one or both the aldehyde and carbon bisulfide may be utilized and any unreacted materials removed by any convenient means from the final product.

Other raft-ios of the compounding ingredients than those mentioned in the examples aswell as other well-known fillers, pigments and the like may be employed in the production of Various types of rubber compounds and are apparent to those skilled in the art to which the invention pertains. The present invention is limited solely by the following claims.

What is claimed is:

1. The process of vulcanizing rubber or a rubber containing material which comprises heating rubber, or a rubber containing material, and sulfur in the presence of a product obtained by reacting a mono N-alkyl cyclohexylamine containing one hydrogen atom on the amino nitrogen atom with an aldehyde in the ratio of substantially two molecular proportions of amine and one of aldehyde, and further reacting the product so obtained with carbon bisulfide.

2. The process of vulcanizing rubber which comprises heating rubber and sulfur in the presence of a product obtained by reacting a mono N-alkyl cyclohexylamine containing one hydrogen atom on the amino nitrogen atom with formaldehyde in the ratio of substantially two molecular proportions of amine and one of formaldehyde and further reacting the product so obtained with carbon bisulfide.

3. The process of vulcanizing rubber which comprises heating rubber and sulfur in the presence of a product obtained by reacting N-methyl cyclohexylamine with an aldehyde in the ratio of substantially two molecular proportions of amine and one of aldehyde and further reacting the product so obtained with carbon bisulfide.

4. The process of vulcanizing rubber which comprises heating rubber and sulfur in the presence of a product obtained by reacting N-methyl cyclohexylamine with formaldehyde in the ratio of substantially two molecular proportions of amine and one of formaldehyde and further reacting the product so obtained with carbon bisulfide.

5. The process of vulcanizing rubber Which comprises heating rubber and sulfur in the presence of a product obtained by reacting N-ethyl cyclohexylamine with formaldehyde in the ratio of substantially two molecular proportions of amine and one of formaldehyde and further reacting the product so obtained with carbon bi- I 6. The vulcanized rubber product obtained by heating rubber or a rubber containing material and sulfur in the presence of a product obtained by reacting a mono N-alkyl cyclohexylamine containing one hydrogen atom on the amino nitrogen atom with an aldehyde in the ratio of substantially two molecular proportions of amine and one of aldehyde and further reacting the product so obtained with carbon bisulfide.

'7. The vulcanized rubber product obtained by heating rubber and sulfur in the presence of a product obtained by reacting a mono N-alkyl cyclohexylamine containing one hydrogen atom on the amino nitrogen atom with formaldehyde in the ratio of substantially two molecular proportions of amine and one of formaldehyde and further reacting the product so obtained with carbon bisulfide.

8. The vulcanized rubber product obtained by heating rubber and sulfur in the presence of a product obtained by reacting N-methyl cyclohexylamine with an aldehyde in the ratio of substantially two molecular proportions of amine and one of aldehyde and further reacting the product so obtained with carbon bisulfide.

9. The vulcanized rubber product obtained by heating rubber and sulfur in the presence of a product obtained by reacting N-methyl cyclohexylamine with formaldehyde in the ratio of substantially two molecular proportions of amine and one of formaldehyde and further reacting the product so obtained with carbon bisulfide.

10. The vulcanized rubber product obtained by heating rubber and sulfur in the presence of a product obtained by reacting N-ethyl cyclohexylamine with formaldehyde in the ratio of substantially two molecular proportions of amine and one of formaldehyde and further reacting the product so obtained with carbon bisulfide.

ROBERT L. SIBLEY. 

